Light emitting device

ABSTRACT

A light emitting device includes a light emitting element adapted to emit a blue light, a sealing resin covering the light emitting element, and a sulfide phosphor-containing layer disposed at an outer side of a sealing resin. The sealing resin contains at least one of a KSF phosphor adapted to absorb a portion of the blue light emitted from the light emitting element to emit red light and a MGF phosphor adapted to absorb a portion of the blue light emitted from the light emitting element to emit red light. The sulfide phosphor-containing layer includes a sulfide phosphor adapted to absorb a portion of the blue light emitted from the light emitting element to emit red light and a MGF phosphor adapted to absorb a portion of the blue light emitted from the light emitting element to emit green light.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This application claims priority to Japanese Patent Application No.2014-206066, filed on Oct. 7, 2014, and No. 2015-196955, filed on Oct.2, 2015. The entire disclosure of Japanese Patent Application No.2014-206066 and No. 2015-196955 are hereby incorporated by reference intheir entireties.

BACKGROUND

1. Technical Field

The present disclosure relates to light emitting devices, and moreparticularly to a light emitting device that includes a light emittingelement configured to emit a blue light, and a sulfide phosphorconfigured to emit a green light upon absorbing a portion of the bluelight emitted from the light emitting element.

2. Description of the Related Art

There have been known light emitting devices adapted to emit a whitelight. This kind of light emitting device includes a light emittingelement to emit a blue light, a green phosphor to emit a green light (ora yellow-green phosphor to emit a yellow-green light) upon absorbing aportion of the blue light emitted from the light emitting element, and ared phosphor to emit a red light upon absorbing a portion of the bluelight emitted from the light emitting element. Such light emittingdevices adapted to emit a white light are used in various applications,such as illumination devices and backlights for various displays, suchas liquid crystal displays.

In recent years, light emitting devices having all or a portion of suchphosphors replaced by a sulfide phosphor have been developed. Forexample, JP 2014-024918 A discloses a white light emitting device thatincludes a green sulfide phosphor and a red phosphor.

Green sulfide phosphors have high light emitting efficiency and anarrower full width at half maximum of the emission spectrum compared tothat of a β-sialon phosphor that is commonly used as a green phosphor.Thus, the light emitting device using a sulfide phosphor has anadvantage of a wide color reproducibility range when combined with acolor filter of a liquid crystal display or the like. Further, matchingthe peak wavelength of the color filter (a wavelength at which itstransmittance reaches a peak) to the emission peak of the sulfidephosphor allows for more light to pass through the color filter, whichimproves the light extraction efficiency with less attenuation of thelight in use of the color filter. Particularly, the green sulfidephosphors have higher light emitting efficiency than that ofconventional green phosphors, allowing for liquid crystal panels of highbrightness.

However, these conventional light emitting devices employing such asulfide phosphor are designed to use a phosphor such as CaS:Eu,(BaSr)₃SiO₅:Eu, or the like, as the red phosphor, which may lead to theoccurrence of secondary absorption. That is, a portion of the greenlight (or the yellow-green light) emitted from the green sulfidephosphor that has absorbed the blue light is absorbed by the redphosphor which then emits a red light. The occurrence of such secondaryabsorption leads to a reduction in the luminous efficiency of the wholelight emitting device. On the other hand, in many applications such asin displays and illumination devices, there has arisen a need for alight emitting device that can emit brighter light with lower powerconsumption, that is, which has high luminance efficiency.

SUMMARY

Certain embodiments of the present invention have been made to meet theforegoing requirements, and it is an object of certain embodiments ofthe present invention to provide a light emitting device that achieveshigh luminous efficiency while utilizing a green sulfide phosphor.

According to one embodiment of the present invention, a light emittingdevice includes a light emitting element adapted to emit a blue light, asealing resin covering the light emitting element, and a sulfidephosphor-containing layer disposed at an outer side of the sealingresin. The sealing resin includes at least one of a KSF phosphor or aMGF phosphor. The KSF phosphor is a compound having the chemical formulaA₂[M_(1−a)Mn⁴⁺ _(a)F₆] (1), where A is at least one selected from thegroup consisting of K⁺, Li⁺, Na⁺, Rb⁺, Cs⁺ and NH⁴⁺, M is at least oneelement selected from the group consisting of Group 4 elements and Group14 elements, and 0<a<0.2; and the KSF phosphor is adapted to absorb atleast a portion of the blue light emitted from the light emittingelement to emit red light. The MGF phosphor is a compound having thechemical formula(x−a)MgO.(a/2)Sc₂O₃.yMgF₂.cCaF₂.(1−b)GeO₂.(b/2)Mt₂O₃:zMn⁴⁻(2), where2.0≦x≦4.0, 0<y<1.5, 0<z<0.05, 0<a≦0.5, 0<b<0.5, 0<c≦1.5, y+c<1.5, and Mtis at least one element selected from Al, Ga and In; and the MGFphosphor is adapted to absorb at least a portion of the blue lightemitted from the light emitting element to emit red light. The sulfidephosphor-containing layer includes a sulfide phosphor having thechemical formula M¹Ga₂S₄:Eu (3) which is a thiogallate phsophoractivated with Eu, where M¹ is at least one selected from Mg, Ca, Sr andBa; and the sulfide phosphor is adapted to absorb at least a portion ofthe blue light emitted from the light emitting element to emit greenlight.

Using the above-described embodiment, a light emitting device thatachieves high luminous efficiency while utilizing a green sulfidephosphor can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view showing a light emittingdevice 100 according to a first embodiment.

FIG. 2 shows preferable chromaticity ranges for light emitted from alight emitting element package 10 on chromaticity coordinate.

FIG. 3A shows a SEM image of a cross section of part of a thus obtainedlight emitting element package 10.

FIG. 3B shows an enlarged SEM image of portion A shown in FIG. 3A.

FIG. 3C shows an enlarged SEM image of portion B shown in FIG. 3A.

FIG. 3D shows an enlarged SEM image of portion C shown in FIG. 3A.

FIG. 3E shows an enlarged SEM image of portion D shown in FIG. 3B.

FIG. 4 shows an emission spectrum of the thus obtained light emittingelement package 10.

FIG. 5A is a schematic cross-sectional view showing an example of aphosphor sheet according to an embodiment of the present invention.

FIG. 5B is a schematic cross-sectional view showing an example of aphosphor sheet according to an embodiment of the present invention.

FIG. 6 is a schematic cross-sectional view showing a liquid crystaldisplay 200 that uses a light emitting device 100B according to a secondembodiment.

FIG. 7 is a schematic cross-sectional view showing a liquid crystaldisplay 300 that uses a light emitting device 100C according to a thirdembodiment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Embodiments according to the present invention will be described belowwith reference to the drawings. It is to be understood that theembodiments described below are intended as illustrative to give aconcrete form to technical ideas of the present invention, and thus thetechnical scope of the invention shall not be limited to those describedbelow. The arrangements illustrated in one embodiment can also beapplied to other embodiments, unless otherwise specified. In thedescription below, if necessary, the terms indicative of the specificdirection or position (for example, “upper”, “lower”, “right”, “left”,and other words including these words) are used for easy understandingof the present invention with reference to the figures. The meanings ofthe terms are not intended to restrict the technical range of thepresent invention. It is understood that in some drawings, the sizes orpositional relationships of members are emphasized to clarify thedescription below and are not limiting. The same parts or members aredesignated by the same reference character throughout the drawings.Further, a member denoted by a combination of a numerical number and aletter, for example, a reference character “10A”, may have the samestructure as that of a member denoted by the same numerical numberwithout any letter, for example, a reference character “10”, or that ofa member denoted by a combination of the same numerical number and adifferent letter unless otherwise specified.

As a result of intensive studies, the inventors have discovered that alight emitting device that uses a green sulfide phosphor can obtain highlight emitting efficiency with the use of at least one of a KSF phosphorand a MGF phosphor as the red phosphor in place of a conventional redphosphor. The KSF phosphors and the MGF phosphors to be described indetail below absorb blue light emitted from a light emitting element andemit red light, and absorb little green light emitted from a greensulfide phosphor. That is, a secondary absorption is substantiallyreduced or does not occur. Thus, the light emitting devices according tocertain embodiments of the present invention have high luminousefficiency. The peak of the emission spectrum of each of the KSFphosphors and the MGF phosphors has a narrow full width at half maximumof about 10 to 20 nm. Accordingly, red light having a narrow full widthat half maximum can be obtained even through a color filter that allowsthe light in the substantially whole red wavelength range to passtherethrough, so that red light of high color purity can be obtained.

Further, a KSF phosphor is contained in the sealing member and disposedcloser to the light emitting element and the sulfide phosphor that hasless robust temperature characteristic is disposed spaced apart from thelight emitting element. Thus, the influence of the heat from the lightemitting element on the sulfide phosphor can be reduced, so thatdegradation of the luminous efficiency can be suppressed.

The KSF phosphor absorbs a small amount of blue light, so that in thecase of obtaining a white light source, a greater amount of the KSFphosphor is needed to be contained than a conventional red phosphor.However, in the case where a KSF phosphor is contained in a phosphorsheet with a green phosphor as described in JP 2014-24918A, thethickness of the phosphor sheet increases due to the large content ofthe KSF phosphor. In the recent backlight light sources, the demand forthinner light sources has progressed and, consequently, the thickness ofthe phosphor sheet must be reduced.

Accordingly, in the certain embodiments of the present invention, theKSF phosphor that is needed in a larger amount than a conventional redphosphor is contained in a sealing member and is disposed close to alight emitting element to reduce the necessary amount of the KSFphosphor to a minimum, while disposing a thermally sensitive sulfidephosphor at an outer side (light extracting side) of the sealing member.With this arrangement, the KSF phosphor can be used without increasingthe thickness of the sulfide phosphor-containing layer (i.e. thephosphor sheet). The reduction in the amount of the phosphor can alsolead to a reduction in the cost. Light emitting devices according toseveral embodiments of the present invention will be described below indetail.

First Representative Embodiment

FIG. 1 shows a schematic cross-sectional view of a light emitting device100 according to a first embodiment. The light emitting device 100includes a light emitting element 1 adapted to emit a blue light, agreen phosphor 24 to absorb a portion of the blue light emitted from thelight emitting element 1 to emit a green light, and a red phosphor 14 toabsorb a portion of the blue light emitted from the light emittingelement 1 to emit a red light. The red phosphor 14 is at least one of aKSF phosphor and a MGF phosphor which will be described in detail below.

In the light emitting device according to the present embodiment, withrespect to the light emitting element 1, the red phosphor 14 is disposedcloser than the green sulfide phosphor 24.

The light emitting device 100 includes a light emitting element package10. The light emitting element package 10 includes a resin package 3having a bottom surface and sidewalls that defining a cavity openingupward, a light emitting element 1 disposed on the bottom surface in thecavity of the resin package 3, and a sealing resin 12 filled in thecavity of the resin package 3. The light emitting element 1 has itspositive electrode and negative electrode connected to an external powersource via conductive members, such as a metal wire, a metal bump or aplated member. Upon being supplied with electric current (electricpower) from the external power source, the light emitting element 1emits a blue light. A lead may be disposed at the bottom surface in thecavity of the resin package 3, and the light emitting element 1 may bedisposed on the lead. In the case of using the lead, the lead may beconnected to the negative electrode and/or the positive electrode by ametal wire, to connect the light emitting element 1 to the externalpower source via the lead. Instead of using the metal wire, flip-chipbonding can be performed with the use of a solder. The lead may have aplated layer on its surface as needed. The sealing resin 12 coverssurfaces of the light emitting element 1 (in the embodiment shown inFIG. 1, the upper surface and the side surfaces of the light emittingelement 1 but not the bottom surface). The sealing resin 12 contains thered phosphor 14. That is, the red phosphor 14 is distributedly arrangedin the sealing rein 12. Note that, although in the embodiment shown inFIG. 1, the red phosphor 14 is uniformly dispersed in the sealing resin12, the form of distribution of the red phosphor is not limited thereto.Alternatively, the red phosphor 14 may be disposed at a higher densityin a portion of the sealing resin 12, for example, may be disposed at ahigh density near the light emitting element 1. One example of such anarrangement can be so-called “sedimentation arrangement” in which, thedistribution density of the red phosphor is smaller at an upper part ofthe sealing resin 12 and higher at the bottom of the sealing resin 12(including a portion directly above the light emitting element 1). Thesedimentation arrangement can be formed, for example, by filling uncuredsealing resin 12 with the red phosphor 14 uniformly distributed thereininto the cavity of the resin package 3, standing the sealing resin 12for a predetermined time while keeping it in the uncured state, allowingthe red phosphor 14 in the sealing resin 12 to settle by gravity, andafter the density of the red phosphor becomes high at the bottom of thesealing resin 12, then, hardening the sealing resin 12. Alternatively,the red phosphors may be settled by a centrifugal force. In addition tothe red phosphors 14, fillers may be distributed in the sealing resin12.

The light emitting element package 10 has its upper surface serving asan emission surface and is configured to emit a blue light and a redlight. More specifically, a portion of the blue light emitted from thelight emitting element 1 passes through the sealing resin 12 and isemitted from the upper surface of the sealing resin 12 to the outside. Aportion of the blue light emitted from the light emitting elementpackage 10 may be reflected at a side surface and/or the bottom surfaceof the resin package 3 while propagating inside the sealing resin 12,and then be emitted from the upper surface of the sealing resin 12.Another portion of the blue light emitted from the light emittingelement 1 may be absorbed in the red phosphor 14 while propagatingthrough the sealing resin 12, whereby the red phosphor 14 is excited toemit a red light. The red light emitted from the red phosphor 14 passesthrough the sealing resin 12 and is emitted from the upper surface ofthe sealing resin 12 toward the outside. A portion of the red lightemitted from the red phosphor 14 is reflected at the side surfacesand/or the bottom surface of the resin package 3 while propagatingthrough the sealing resin 12, and then is emitted from the upper surfaceof the sealing resin 12.

A green sulfide phosphor-containing layer 20 is disposed at an outerside of the sealing resin 12, that is, in FIG. 1, over the sealing resin12 (or resin package 3). The green sulfide phosphor-containing layer 20includes a light-transmissive material 22 and the green sulfide phosphor24. That is, the green sulfide phosphor 24 is distributedly arranged inthe light-transmissive material 22. The green sulfidephosphor-containing layer 20 may have any appropriate form. Onepreferable form of the green phosphor-containing layer 20 is a sheetshape (or film shape) as shown in FIG. 1. This is because the thicknessof the green sulfide phosphor-containing layer 20 can be made uniform tosuppress color unevenness.

With this arrangement, in the light emitting device 100, with respect tothe light emitting element 1, the red phosphor 14 is disposed closerthan the green sulfide phosphor 24. The KSF phosphor or the MGFphosphor, which is required in a greater amount than the green sulfidephosphor for wavelength conversion, is disposed closer to the lightemitting element and the green sulfide phosphor is disposed farther fromthe light emitting element 1. Thus, the necessary amount of the redphosphor can be reduced, which leads to further improvement in the lightextraction efficiency (that is, light emitting efficiency).

A large portion of the red light emitted from the upper surface of thelight emitting element package 10 propagates into the green sulfidephosphor-containing layer 20 from its lower surface, passes through thelight-transmissive material 22 of the green sulfide phosphor-containinglayer 20, and then exits from the upper surface of the green sulfidephosphor-containing layer 20 to the outside. A large portion of the bluelight emitted from the upper surface of the light emitting elementpackage 10 enters the green sulfide phosphor-containing layer 20 fromits lower surface. A portion of the blue light that has entered thegreen sulfide phosphor-containing layer 20 from the lower surface passesthrough the light-transmissive material 22 of the green sulfidephosphor-containing layer 20, and then exits from the upper surface ofthe green sulfide phosphor-containing layer 20 to the outside. Anotherportion of the blue light that has entered the green sulfidephosphor-containing layer 20 from its lower surface is partiallyabsorbed in the green sulfide phosphor 24, whereby the green sulfidephosphor 24 emits green light. A large portion of the green lightemitted from the green sulfide phosphor 24 propagates through thelight-transmissive material 22 and then exits from the upper surface ofthe green sulfide phosphor-containing layer 20 to the outside. As aresult, a white light that is a mixture of the blue light, the redlight, and the green light can be obtained outside the upper surface ofthe green sulfide phosphor-containing layer 20.

Note that a portion of the green light emitted from the green sulfidephosphor 24 propagates downward and exits from the lower surface of thegreen sulfide phosphor-containing layer 20, and then enters the sealingresin 12 from the upper surface of the light emitting element package10. However, the red phosphor 14, which is at least one of a KSFphosphor and a MGF phosphor, absorbs little green light. Accordingly, aportion of green light emitted from the upper surface of the greensulfide phosphor-containing layer 20 may be the light, for example, thatis reflected at the inner surface of the resin package 3 and emittedfrom the upper surface of the light emitting element package 10, thenenters the green sulfide phosphor-containing layer 20 from its lowersurface and then is emitted from the upper surface of the green sulfidephosphor-containing layer 20. The presence of such green lightcontributes to improving the light extraction efficiency of the lightemitting device 100.

In the embodiment shown in FIG. 1, the green sulfide phosphor-containinglayer 20 and the sealing resin 12 (or resin package 3) are spaced apartfrom each other. Thus, the light emitting device can have the effect ofmore surely suppressing the transfer of heat generated from the lightemitting element 1 to the green sulfide phosphor 24, which is sensitiveto heat. The arrangement, however, is not limited thereto, andalternatively, the green sulfide phosphor-containing layer 20 and thesealing resin 12 (or resin package 3) may be in contact with each other.In this case, a larger amount of light emitted from the light emittingelement package 10 is allowed to enter the green sulfidephosphor-containing layer 20, so that the light extraction efficiencycan be further improved. Moreover, even in the case where the greensulfide phosphor-containing layer 20 is in contact with the sealingresin 12 (or resin package 3), the light emitting element 1 is spacedapart from the green sulfide phosphor 24 to some degree, so that thermaldegradation of the green sulfide phosphor 24 can be suppressed.

In the embodiment shown in FIG. 1, the light emitting element package 10is a top-view type package in which the mounting surface is the bottomsurface (lower surface); that is, the mounting surface is at theopposite side to the light extraction surface (for example, the uppersurface serves as the light extraction surface and the lower surfaceserves as the mounting surface). However, the light emitting elementpackage 10 is not limited thereto, and the light emitting elementpackage 10 may be structured as a so-called side view type, in which asurface adjacent to the light extraction surface serves as the mountingsurface. In the embodiment shown in FIG. 1, the light emitting elementpackage 10 that includes the resin package 3 is used, but the lightemitting device is not limited thereto. In place of the light emittingelement package 10, a so-called “packageless type” may be employed, inwhich a phosphor layer containing the red phosphor 14 is formed on thesurface of the light emitting element 1 without having a resin package.

FIG. 2 is a diagram showing preferable chromaticity ranges of the lightemitted from embodiments of the light emitting element package 10 (i.e.the light entering the green sulfide phosphor-containing layer 20) onchromaticity coordinates. The chromaticity of light emitted from thelight emitting element package 10 is preferably in a quadrangular regionindicated by dashed lines in FIG. 2 (i.e. a quadrangular region formedby connecting four points of (0.4066, 0.1532), (0.3858, 0.1848),(0.1866, 0.0983) and (0.1706, 0.0157) on an x-y chromaticity coordinatesystem of a CIE1931 chromaticity diagram). The chromaticity of lightemitted from the light emitting element package 10 is more preferably ina quadrangular region indicated by solid lines in FIG. 2 (i.e. aquadrangular region formed by connecting four points of (0.19, 0.0997),(0.19, 0.027013), (0.3, 0.09111) and (0.3, 0.014753) on an x-ychromaticity coordinate system of a CIE1931 chromaticity diagram). Withthe chromaticity within such regions, under the presence of the greensulfide phosphor-containing layer 20, a color tone suitable for backlight can be achieved.

A light emitting element package 10 to emit light of the chromaticitywithin those regions were prepared and the emission spectrum weremeasured, as described below. FIG. 3A shows a SEM image of a crosssection of a portion of the light emitting element package 10. FIG. 3Bshows an enlarged SEM image of the portion A shown in FIG. 3A. FIG. 3Cshows an enlarged SEM image of the portion B shown in FIG. 3A. FIG. 3Dshows an enlarged SEM image of the portion C shown in FIG. 3A, and FIG.3E shows an enlarged SEM image of the portion D shown in FIG. 3B. Aresin package 3 was provided with a cavity defined in a substantiallysquare shape with rounded corners in the top view, with an outsidedimensions of 4 mm in length, 1.4 mm in width and 0.6 mm in height. Theresin package 3 was provided with a pair of leads 5 on the bottom in thecavity, and each of the leads 5 had a plated layer on its surfaces. Alight emitting element 1 having a light-transmissive substrate 13 and asemiconductor layer 11 was disposed on one of the pair of leads 5. Thelight emitting element 1 was electrically connected to the pair of leads5 by gold wires, respectively.

The sealing resin 12 was disposed such that a silicon resin having thered phosphor 14 and the filler 16 distributed therein was disposed inthe cavity of the resin package 3, and then, the red phosphor 14 and thefiller 16 were centrifugally sedimented to form a sealing resin 12. Forthe red phosphor 14, a KSF phosphor (K₂MnF₆:Mn⁴⁺) was used. For thefiller 16, a silica filler and a nanosilica filler were used. Thesealing resin 12 contained about 17 parts by weight of a KSF phosphor,about 5 parts by weight of a silica filler and about 0.4 parts by weightof a nanosilica filler with respect to 100 parts by weight of thesilicone resin. As shown in FIG. 3C, an upper portion of a side surfaceof the light emitting element 1 was covered with neither the redphosphor 14 nor the filler 16.

FIG. 4 shows an emission spectrum of the light emitting element package10 thus obtained. The light emitting element 1 emits light of awavelength mainly between 430 nm and 480, and the red phosphor 14 emitslight of a wavelength mainly between 600 nm and 660. The emissionspectrum has a first peak wavelength at 447 nm at which the highestemission intensity is obtained, and a second peak wavelength at 631 nmat which the highest emission intensity of the red phosphor 14 isobtained. The ratio of the emission intensity at the first wavelength ofthe emission peak to the emission intensity at the second wavelength ofthe emission peak is 100:67 (i.e. the first emission intensity:thesecond emission intensity=100:67). The values of chromaticitycoordinates in the CIE1931 system were x=0.216 and y=0.054.

Next, the respective elements of the light emitting device 100 will bedescribed in detail.

1) Light Emitting Element

The light emitting element 1 may be of any appropriate known lightemitting element or blue LED chip, as long as it can emit a blue light(with the emission peak wavelength in a range of 435 to 465 nm). Thelight emitting element 1 may include a semiconductor stacked-layer body,and preferably includes a nitride semiconductor stacked-layer body. Thesemiconductor stacked-layer body (preferably, nitride semiconductorstacked-layer body) may include a first semiconductor layer (forexample, an n-type semiconductor layer), an emission layer, and a secondsemiconductor layer (for example, a p-type semiconductor layer) in thisorder. More specifically, In_(X)Al_(Y)Ga_(1-X-Y)N (0≦X, 0≦Y, X+Y≦1) maybe suitably used for a nitride semiconductor material. The thickness andthe layer structure of each layer may be those known in the art.

2) Red Phosphor

The red phosphor 14 is at least one of a KSF phosphor and a MGFphosphor. The KSF phosphors and the MGF phosphors barely absorb greenlight, and thus are advantageous that secondary absorption barelyoccurs. The red phosphors have a half-width of the emission peak of 35nm or less, and preferably 10 nm or less. The particle diameter is, forexample, 20 to 50 μm (average particle diameter). In the presentspecification, the value of the average particle diameter is indicatedas a F.S.S.S.No (Fisher Sub Sieve Sizer's No) that is determined byusing an air permeable method. The KSF phosphors and the MGF phosphorswill be described in detail below.

(KSF Phosphor)

The KSF phosphors are a red phosphor having the wavelength of theemission peak in a range of 610 to 650 nm. The composition of the KSFphosphors is represented by the following chemical formula (1):

A₂[M_(1−a)Mn⁴⁺ _(a)F₆]  (1)

where A is at least one selected from the group consisting of K⁺, Li⁺,Na⁺, Rb⁺, Cs⁺ and NH⁴⁺; M is at least one element selected from thegroup consisting of Group 4 elements and Group 14 elements; and 0<a<0.2.

The full width at half maximum of the emission peak of the KSF phosphoris 10 nm or less. Examples of KSF phosphors are disclosed by JapanesePatent Application No. 2014-122887 and U.S. Pat. No. 9,120,972, filed bythe applicant of the present application. The entire contents ofJapanese Patent Application No. 2014-122887 and U.S. Pat. No. 9,120,972are incorporated herein by reference.

One embodiment of a method of manufacturing a KSF phosphor will bedescribed below. First, KHF₂ and K₂MnF₆ are weighed to attain a desiredcomposition ratio. The weighed KHF₂ is dissolved in an HF aqueoussolution thereby preparing a solution A. The weighed K₂MnF₆ is dissolvedin the HF aqueous solution, thereby preparing a solution B. Further, anaqueous solution containing H₂SiF₆ is prepared to attain a desiredcomposition ratio, producing a solution C containing the H₂SiF₆. Each ofthe solutions B and C is dripped into the solution A while stirring thesolution A at room temperature. The solution containing the thusobtained precipitate is subjected to solid-liquid separation, washedwith ethanol, and then dried to produce a KSF phosphor.

(MGF Phosphor)

The MGF phosphors are red phosphors that emit a deep-red fluorescence.That is, the MGF phosphors are activated with Mn⁴⁺ and have a wavelengthof the emission peak of 650 nm or more, which is located at a longerwavelength side than the peak emission wavelength of the KSF phosphors.One example of the composition of the MGF phosphors is represented bythe following chemical formula: 3.5MgO.0.5MgF₂.GeO₂:Mn⁴⁺. The MGFphosphors have a full width at half maximum of 15 nm to 35 nm.

In the MGF phosphors, Mg in MgO in the composition may be partiallysubstituted by another element, such as Li, Na, K, Sc, Y, La, Ce, Pr,Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, V, Nb, Ta, Cr, Mo, W, orthe like, and/or the Ge in GeO₂ may be partially substituted by anotherelement, such as B, Al, Ga, In, or the like, in order to improve theluminous efficiency. It is preferable that substituting Mg and Ge by Scand Ga, respectively, can further improve the emission intensity oflight in a wavelength range of 600 to 670 nm, which is called a deepred.

The MGF phosphors are represented by the following chemical formula (2):

(x−a)MgO.(a/2)Sc₂O₃ .yMgF₂ .cCaF₂.(1−b)GeO₂.(b/2)Mt₂O₃:zMn⁴⁺  (2)

where x, y, z, a, b and c satisfy 2.0≦x≦4.0, 0<y<1.5, 0<z<0.05, 0≦a<0.5,0<b<0.5, 0<c≦1.5 and y+c<1.5, and Mt is at least one element selectedfrom Al, Ga and In.

In the chemical formula (2), a and b are set to satisfy 0.05≦a<0.3 and0.05≦b<0.3. Thus, the brightness of the emitted red light can beimproved. Examples of MGF phosphors are disclosed by Japanese PatentApplication No. 2014-113515, filed by the applicant of the presentapplication. The entire contents of Japanese Patent Application No.2014-113515 is incorporated herein by reference.

One embodiment of a method of manufacturing a MGF phosphor in theembodiment of the present invention will be described below. First, MgO,MgF₂, Sc₂O₃, GeO₂, Ga₂O₃, and MnCO₃ are weighed as raw materials toattain the desired composition ratio. After mixing these raw materialstogether, the mixture is charged into a cruicible and calcined at atemperature of 1000 to 1300° C. under atmosphere, thus producing a MGFphosphor. The ratio of the emission intensity at the peak wavelength ofthe light emitting element to the emission intensity at the peakwavelength the red phosphor is preferably 100:55 to 70 (i.e. thefirst:the second=100:55 to 70).

3) Green Sulfide Phosphor

The green sulfide phosphor 24 is a phosphor represented by the chemicalformula (3):

M¹Ga₂S₄:Eu   (3)

(3) is a thiogallate phsophor activated with Eu where M¹ is at least oneselected from Mg, Ca, Sr and Ba. The green sulfide phosphor 24 may havea particle size (average particle size), for example, of 5 to 20 μm. Thegreen sulfide phosphor 24 emits a green light having a wavelength of theemission peak in a range of e.g., 520 to 560 nm. A full width at halfmaximum of the emission peak wavelength of the green sulfide phosphor 24may be 55 nm or less and preferably 50 nm or less.

4) Light-Transmissive Material

The light-transmissive material 22 allows the blue light, the greenlight and the red light to pass therethrough. The light-transmissivematerial allows transmittance of preferably 60% or more, more preferably70% or more, still more preferably 80% or more, and most preferably 90%or more of the light emitted from the light emitting element 1 andincident on the light-transmissive material 22. Examples of suitablelight-transmissive material 22 include, high strain point glass, sodaglass (Na₂O.CaO.SiO₂), borosilicate glass (Na₂O.B₂O₃.SiO₂), forsterote(2MgO.SiO₂), lead glass (Na₂O.PbO.SiO₂), and alkali-free glass. Examplesof suitable light-transmissive material 22 also include organic polymers(that may take the forms of polymer material, such as a plastic film, aplastic sheet, and a plastic substrate, each of which is made of apolymer material and has flexibility), the examples include, apolymethyl methacrylate (PMMA), a polyvinyl alcohol (PVA), a polyvinylphenol (PVP), a polyethersulfone (PES), a polyimide, a polycarbonate(PC), a polyethylene terephthalate (PET), a polystyrene (PS), apolyethylene naphthalate (PEN), a cyclic amorphous polyolefin, amultifunctional acrylate, a multifunctional polyolefin, an unsaturatedpolyester, an epoxy resin and a silicone resin.

For example, in the case of forming in a sheet shape, the sheet may be asingle sheet containing a sulfide phosphor as shown in FIG. 1, or thesheet containing a sulfide phosphor may be disposed between twotransparent layers as shown in FIG. 5A. For example, the phosphor sheet23 shown in FIG. 5A can be fabricated such that, a sulfidephosphor-containing resin composition is disposed on a transparent layer25 to form a green sulfide phosphor-containing layer 20 and anothertransparent layer 25 is stacked on the green sulfide phosphor-containinglayer 20. Alternatively, the phosphor sheet 23 having a structure shownin FIG. 5B can be fabricated such that, a phosphor sheet 23 is placedbetween two sealing films 27 a and 27 b and the whole is thermallycompressed.

The green sulfide phosphor-containing layer has a thickness ofpreferably 10 to 100 μm, more preferably 20 to 40 μm.

For the transparent layer 25, a thermoplastic resin film, athermosetting resin film, or an optically curable resin film with athickness of 10 to 100 μm can be used. Examples thereof include apolyester film, a polyamide film, a triacetylcellulose film, and apolyolefin film. In order to improve adhesion to the phosphor-containingresin compound, the surfaces of those films may be subjected to a plasmatreatment as needed.

5) Sealing Resin

The sealing resin 12 allows the blue light and the red light to passtherethrough, and preferably also allows the green light to passtherethrough. The light-transmissive material allows transmittance ofpreferably 60% or more, more preferably 70% or more, still morepreferably 80% or more, and most preferably 90% or more of the lightemitted from the light emitting element 1 and incident on thelight-transmissive material 22. Examples of suitable materials for thesealing resin 12 include, a silicone resin, a modified silicone resin,an epoxy resin, a modified epoxy resin, a phenol resin, a polycarbonateresin, an acrylic resin, a TPX resin, a polynorbornene resin, or ahybrid resin containing one or more kinds of these resins. Of theseresins, the silicone resin or epoxy resin is preferable, because of itsgood resistance to light and heat. The epoxy resin is also a preferableresin.

6) Resin Package

The resin package 3 may be formed of any suitable resin. Examples ofpreferable resins include, a thermoplastic resin containing at least oneof an aromatic polyamide resin, a polyester resin, and a liquid crystalresin; or a thermosetting resin containing at least one of an epoxyresin, a modified epoxy resin, a phenol resin, a silicone resin, amodified silicone resin, a hybrid resin, an acrylate resin, a urethaneresin. The resin package 3 is preferably formed of a white resin. Thisis because more of the light propagates through the sealing resin 12 andreaches the resin package 3 can be reflected.

Second Representative Embodiment

FIG. 6 is a schematic cross-sectional view showing a liquid crystaldisplay 200 that has a light emitting device 100B according to a secondembodiment. The light emitting device 100B includes the light emittingelement package 10, the green sulfide phosphor-containing layer 20, anda light guide plate 52 disposed between the light emitting elementpackage 10 and the green sulfide phosphor-containing layer 20. In theembodiment shown in FIG. 6, the light guide plate 52 is disposed betweenthe sealing resin 12 of the light emitting element package 10 and thegreen sulfide phosphor-containing layer 20. More specifically, thesealing resin 12 is arranged facing one side surface of the light guideplate 52, and the green sulfide phosphor-containing layer 20 is disposedfacing the upper surface of the light guide plate 52. In the embodimentshown in FIG. 6, the light emitting element package 10 is of a top-viewtype, but is not limited thereto, and may have any other form, such asthe side-view type described above.

The light emitting device 100B may include a reflecting plate(reflector) 51 on the lower surface of the light guide plate 52 toupwardly reflect a portion of the light entering the light guide plate52 through the light emitting element package 10 and reaching the lowersurface of the light guide plate 52, and then to direct the reflectedlight toward the upper surface of the light guide plate 52.

In the embodiment shown in FIG. 6, the light emitting element package 10is disposed spaced apart from the light guide plate 52, but is notlimited thereto. The light emitting element package 10 and the lightguide plate 52 may be arranged in contact with each other by, forexample, arranging the sealing resin 12 or the resin package 3 incontact with the side surface of the light guide plate 52. The greensulfide phosphor-containing layer 20 may be arranged in contact with theupper surface of the light guide plate 52, or spaced apart from thelight guide plate 52.

A lower polarizing film 53A is disposed on the green sulfidephosphor-containing layer 20. A liquid crystal cell 54 is disposed onthe lower polarizing film 53A, and a color filter array 55 is disposedon the liquid crystal cell 54. The color filter array 55 includes aplurality of kinds of color filter portions corresponding to differentcolors, each filter portion allowing only the light of a specific colorto pass therethrough. The color filter portions include, for example,red color filter portions 55A, green color filter portions 55B and bluecolor filter portions 55C. An upper polarizing film 53B is disposed onthe color filter array 55.

Next, the operation of the liquid crystal display 200 will be described.A portion of blue light emitted from the light emitting element 1 exitsfrom the sealing resin 12. Another portion of the blue light emittedfrom the light emitting element 1 is absorbed in the red phosphor 14disposed in the sealing resin 12, and then red light is emitted from thered phosphor 14. The red light emitted from the red phosphor 14 exitsthrough the sealing resin 12. That is, a purple light, which is amixture of the blue light and the red light, is emitted from the lightemitting element package 10. The purple light (blue light+red light)enters the green sulfide phosphor-containing layer 20 via the lightguide plate 52. A portion of the blue light entering the green sulfidephosphor-containing layer 20 is absorbed in the green sulfide phosphor24, whereby the green sulfide phosphor 24 emits a green light. As aresult, a white light which is a mixture of the blue light, the greenlight, and the red light is emitted from the upper surface of the greensulfide phosphor-containing layer 20, and the white light enters a lowerpolarizing film 53A. A portion of the white light (blue light+greenlight+red light) entering the lower polarizing film 53A passes throughthe lower polarizing film 53A to enter the liquid crystal cell 54. Aportion of the white light entering the liquid crystal cell 54 passesthrough the liquid crystal cell 54 to reach the color filter array 55.Further, by providing a prism sheet and/or a film for improving theluminance between the green sulfide phosphor-containing layer 20 and thelower polarizing film 53A, efficient conversion of the blue light can beachieved, so that a desired chromaticity can be obtained with smalleramounts of the phosphors.

The blue light, the green light and the red light reaching the colorfilter array 55 can pass through the corresponding filter portion. Forexample, the red light passes through the red color filter portions 55A,the green light passes through the green color filter portions 55B, andthe blue light passes through the blue color filter portions 55C. Eachof the blue, green and red lights passing through the color filter array55 can partially pass through the upper polarizing film 53B. In thisway, the liquid crystal display 200 can display a desired image. Asdescribed above, each of the red light emitted from the red phosphor 14and the green light emitted from the green sulfide phosphor 24 has anarrow full width at half maximum of the emission peak, and thus has thehigh color purity. Also, a larger amount of light can pass through thered color filter portions 55A and the green color filter portions 55B,so that the luminous efficiency can be improved.

Third Representative Embodiment

In the second embodiment, an edge-type liquid crystal display isillustrated, but similar effects can be also obtained in a direct-typeliquid crystal display. FIG. 7 is a schematic cross-sectional viewshowing a liquid crystal display 300 that has a light emitting device100C according to a third embodiment. The light emitting device 100Bincludes the light emitting element package 10, the green sulfidephosphor-containing layer 20, and a diffusion plate 56 disposed betweenthe light emitting element package 10 and the green sulfidephosphor-containing layer 20. In the case of a direct-type liquidcrystal display, a diffusion plate 56 may be disposed between thesealing resin 12 and the sulfide phosphor-containing layer 20 and spacedapart from the sealing resin 12.

Although the disclosure has been described with reference to severalexemplary embodiments, it shall be understood that the words that havebeen used are words of description and illustration, rather than wordsof limitation. Changes may be made within the purview of the appendedclaims, as presently stated and as amended, without departing from thescope and spirit of the disclosure in its aspects. Although thedisclosure has been described with reference to particular examples,means, and embodiments, the disclosure may be not intended to be limitedto the particulars disclosed; rather the disclosure extends to allfunctionally equivalent structures, methods, and uses such as are withinthe scope of the appended claims.

The illustrations of the examples and embodiments described herein areintended to provide a general understanding of the various embodiments,and many other examples and embodiments may be apparent to those ofskill in the art upon reviewing the disclosure. Other embodiments may beutilized and derived from the disclosure, such that structural andlogical substitutions and changes may be made without departing from thescope of the disclosure. Additionally, the illustrations are merelyrepresentational and may not be drawn to scale. Certain proportionswithin the illustrations may be exaggerated, while other proportions maybe minimized. Accordingly, the disclosure and the figures are to beregarded as illustrative rather than restrictive.

One or more examples or embodiments of the disclosure may be referred toherein, individually and/or collectively, by the term “invention” merelyfor convenience and without intending to voluntarily limit the scope ofthis application to any particular disclosure or inventive concept.Moreover, although specific examples and embodiments have beenillustrated and described herein, it should be appreciated that anysubsequent arrangement designed to achieve the same or similar purposemay be substituted for the specific examples or embodiments shown. Thisdisclosure may be intended to cover any and all subsequent adaptationsor variations of various examples and embodiments. Combinations of theabove examples and embodiments, and other examples and embodiments notspecifically described herein, will be apparent to those of skill in theart upon reviewing the description.

In addition, in the foregoing Detailed Description, various features maybe grouped together or described in a single embodiment for the purposeof streamlining the disclosure. This disclosure may be not to beinterpreted as reflecting an intention that the claimed embodimentsrequire more features than are expressly recited in each claim. Rather,as the following claims reflect, inventive subject matter may bedirected to less than all of the features of any of the disclosedembodiments. Thus, the following claims are incorporated into theDetailed Description, with each claim standing on its own as definingseparately claimed subject matter.

The above disclosed subject matter shall be considered illustrative, andnot restrictive, and the appended claims are intended to cover all suchmodifications, enhancements, and other embodiments which fall within thetrue spirit and scope of the present disclosure. Thus, to the maximumextent allowed by law, the scope of the present disclosure may bedetermined by the broadest permissible interpretation of the followingclaims and their equivalents, and shall not be restricted or limited bythe foregoing detailed description.

All of the publications, patent applications and patents cited hereinare incorporated herein by reference in their entirety.

What is claimed is:
 1. A device comprising: a light emitting devicecomprising: a light emitting element adapted to emit a blue light, asealing resin covering the light emitting element, and a sulfidephosphor-containing layer disposed separate from the sealing resin; anda light guide plate, wherein the sealing resin includes one or both of:(i) a KSF phosphor, wherein the KSF phosphor is a compound having thechemical formula:A₂ [M_(1−a)Mn⁴⁺ _(a)F₆] where A is at least one selected from the groupconsisting of K⁺, Li⁺, Na⁺, Rb⁺, Cs⁺and NH⁴⁺, M is at least one elementselected from the group consisting of Group 4 elements and Group 14elements, and 0<a<0.2; and the KSF phosphor is adapted to absorb atleast a portion of the blue light emitted from the light emittingelement to emit red light, and (ii) a MGF phosphor, wherein the MGFphosphor is a compound having the chemical formula:(x−a)MgO.(a/2)Sc₂O₃ .yMgF₂ .cCaF₂.(1−b)GeO₂.(b/2)Mt₂O₃:zMn⁴⁺ where2.0≦x≦4.0, 0<y<1.5, 0<z<0.05, 0≦a<0.5, 0<b<0.5, 0≦c<1.5 y+c <1.5, and Mtis at least one element selected from Al, Ga and In, and the MGFphosphor is adapted to absorb at least a portion of the blue lightemitted from the light emitting element to emit red light; and whereinthe sulfide phosphor-containing layer includes a sulfide phosphor havingthe chemical formula:M¹Ga₂S₄:Eu which is a thiogallate phsophor activated with Eu, where M¹is at least one selected from Mg, Ca, Sr and Ba, and the sulfidephosphor is adapted to absorb at least a portion of the blue lightemitted from the light emitting element to emit green light, wherein thesealing resin is disposed facing a lateral surface of the light guideplate, and the sulfide phosphor-containing layer is disposed facing anupper surface of the light guide plate.
 2. The device according to claim1, wherein the sulfide phosphor-containing layer is formed in a sheetshape.
 3. The device according to claim 1, wherein the sulfidephosphor-containing layer has a thickness of 20 to 40 μm.
 4. The deviceaccording to claim 1, wherein the light emitting element and the sealingresin are parts of a light emitting element package that is separatefrom the sulfide phosphor-containing layer.
 5. The device according toclaim 4, wherein: the light emitting device further comprises a packagehaving a bottom surface and sidewalls that define a cavity, the lightemitting element is disposed on the bottom surface of the package, andthe sealing resin is disposed in the cavity of the package.
 6. Thedevice according to claim 4, wherein a chromaticity of light emittedfrom the light emitting device is in a quadrangular region formed byconnecting four points of (0.4066, 0.1532), (0.3858, 0.1848), (0.1866,0.0983) and (0.1706, 0.0157) on an x-y chromaticity coordinate system ofa CIE1931 chromaticity diagram.
 7. The device according to claim 4,wherein a chromaticity of light emitted from the light emitting deviceis in a quadrangular region formed by connecting four points of (0.19,0.0997), (0.19, 0.027013), (0.3, 0.09111) and (0.3, 0.014753) on an x-ychromaticity coordinate system of a CIE1931 chromaticity diagram.
 8. Thedevice according to claim 1, wherein the sealing resin includes the KSFphosphor.
 9. The device according to claim 8, wherein the KSF phosphoris K₂MnF₆:Mn⁴⁺.
 10. The device according to claim 8, wherein an averageparticle diameter of the KSF phosphor is in a range of 20 to 50 μm. 11.The device according to claim 8, wherein the KSF phosphor has a peakemission wavelength in a range of 610 to 650 nm.
 12. The deviceaccording to claim 8, wherein a full width at half maximum of theemission peak of the KSF phosphor is 10 nm or less.
 13. The deviceaccording to claim 1, wherein the sealing resin includes the MGFphosphor.
 14. The device according to claim 13, wherein the MGF phosphoris 3.5Mg.0.5MgF₂.GeO₂:Mn⁴⁺.
 15. The device according to claim 13,wherein an average particle diameter of the MGF phosphor is in a rangeof 20 to 50 μm.
 16. The device according to claim 13, wherein the MGFphosphor has a peak emission wavelength of 650 nm or more.
 17. Thedevice according to claim 13, wherein a full width at half maximum ofthe emission peak of the MGF phosphor is in a range of 15 to 35 nm. 18.The device according to claim 1, wherein an average particle size of thesulfide phosphor is in a range of 5 to 20 μm.
 19. The device accordingto claim 1, wherein the sulfide phosphor has a peak emission wavelengthin a range of 520 to 560 nm.
 20. The device according to claim 1,wherein a full width at half maximum of the emission peak of the sulfidephosphor is 55 nm or less.
 21. The device according to claim 1, whereina full width at half maximum of the emission peak of the sulfidephosphor is 50 nm or less.
 22. The device according to claim 1, furthercomprising: a polarizing film disposed on the sulfidephosphor-containing layer; a liquid crystal cell disposed on thepolarizing film; and a color filter array disposed on the liquid crystalcell.
 23. A device comprising: a light emitting device comprising: alight emitting element adapted to emit a blue light, a sealing resincovering the light emitting element, and a sulfide phosphor-containinglayer disposed separate from the sealing resin; and a diffusion platedisposed between the sealing resin and the phosphor-containing layer,the diffusion plate being spaced apart from the sealing resin, whereinthe sealing resin includes one or both of: (i) a KSF phosphor, whereinthe KSF phosphor is a compound having the chemical formula:A₂ [M_(1−a)Mn⁴⁺ _(a)F₆] where A is at least one selected from the groupconsisting of K⁺, Li⁺, Na⁺, Rb⁺, Cs⁺and NH⁴⁺, M is at least one elementselected from the group consisting of Group 4 elements and Group 14elements, and 0<a<0.2; and the KSF phosphor is adapted to absorb atleast a portion of the blue light emitted from the light emittingelement to emit red light, and (ii) a MGF phosphor, wherein the MGFphosphor is a compound having the chemical formula:(x−a)MgO.(a/2)Sc₂O₃ .yMgF₂ .cCaF₂.(1−b)GeO₂.(b/2)Mt₂O₃:zMn⁴⁺ where2.0≦x≦4.0, 0<y<1.5, 0<z<0.05, 0≦a<0.5, 0<b<0.5, 0≦c<1.5 y+c <1.5, and Mtis at least one element selected from Al, Ga and In, and the MGFphosphor is adapted to absorb at least a portion of the blue lightemitted from the light emitting element to emit red light; and whereinthe sulfide phosphor-containing layer includes a sulfide phosphor havingthe chemical formula:M¹Ga₂S₄:Eu which is a thiogallate phsophor activated with Eu, where M¹is at least one selected from Mg, Ca, Sr and Ba, and the sulfidephosphor is adapted to absorb at least a portion of the blue lightemitted from the light emitting element to emit green light.